The present invention relates to a micro-pulsation metering fuel injection system, particularly to a micro-pulsation metering fuel injection system to be used in an internal combustion engine.
Fuel supply systems of conventional internal combustion engines include carburetors and electrical fuel injection systems. As shown in FIG. 8, a mechanical carburetor 60, using under pressure generated by flow in a tube, sucks in and atomizes fuel. The carburetor 60 mainly comprises a throttle body 70, controlling inflow of air, and an adjustment needle 61, controlling intake of fuel. Atomized fuel, having mixed with air, enters cylinders of the internal combustion engine. As shown in FIG. 9, an electrical injection system has an electric fuel pump 80. The electric fuel pump 80 pressurizes fuel, which is subsequently pushed out through an injector 81 and by mechanical force ripped apart into a fuel beam and fuel droplets, entering an inlet manifold 71 at high pressure. Thus fuel droplets are injected into cylinders of the internal combustion engine in air inducing process.
However, conventional carburetors developed to the present day have become complicated precision devices, which makes manufacturing thereof difficult and expensive. Being regulated by an inclination of the adjustment needle and flow control by the throttle valve, the quantity of fuel taken in is not easy controlled. There is also no way to regulate the quantity of fuel taken in by computer control, nor to accommodate a widely varying pattern of demand for fuel, while maintaining a proper fuel-to-air ratio. Furthermore, using a throttle valve results in imperfect atomization, so that wall-wetting happen in the inlet pipes of the cylinders. For these reasons, conventional carburetors, while being complicated and expensive, are not able to control combustion in the engine.
On the other hand, a fuel injection system, requiring a pressurizing pump, a high-pressure pipe, a regulating valve, a pressure stabilizer and an injector has a large number of structural parts. Since working pressure closests 3 kg/m2, sealing pipes and the pump requires special attention to prevent leakage. Therefore, a fuel injection system is expensive to make and thus only used in cars and heavy motorcycles. In these, electrical fuel injection systems are frequently encountered, but for light motorcycles only a small number of manufacturers have considered using fuel injection systems.
Concerning safety, since a fuel injection system has pipes under pressure, a collision or burst of the pipes for another reason causes a fuel jet to spurt out at high speed, forming fuel vapor which is readily ignited by a spark or heat (e.g. of a catalytic converter). This is a severe safety drawback.
Although fuel injection systems, by using electric control, precisely maintain a proper fuel-to-air ratio, ejection of fuel at high pressure and speed results in fuel droplets of nonuniform sizes (usually more than 100xcexc SMD-sault mean dia), so that fuel does not completely mix with air. Being ejected at high speed (over 20 m/sec), fuel first hits the wall of the inlet pipe, aggravating the problem of wetted walls and unused fuel.
Due to great progress of micromechanical and microelectronics production processes in recent years, along with research on a large scale, micropumps have been commercialized in inkjet printers, constituting the richest and greatest product and technique for research in fuel injection systems.
The main area of application of micropumps are printer heads. There are two types, thermal bubble and piezoelectric micropumps. A thermal bubble micropump, as shown in FIG. 6, has a silicon substrate 1, on which a polycrystalline silicon layer 2 is laid, with insulation layers 8, 9 placed in between. Metal wires 7 run along between the insulation layers 8 and 9. A dry film 3 is spread on the polycrystalline silicon layer 2. A flow path and an electric circuit are engraved into the dry film 3, so that a plurality of ejection chambers 4 are formed. A nozzle plate 5 is glued on the dry film 3. The nozzle plate 5 is made by galvanic patterns and has ejection holes 6 that correspond to the ejection chambers 4. Liquid flows through flow paths into ejection chambers 4, then heat is generated by an electric current through the layer below the polycrystalline silicon layer 2, causing liquid in ejection chambers 4 to evaporate, forming bubbles which drive out liquid through the ejection holes 6.
A piezoelectric micropump, as shown in FIG. 7, has a substrate 1A on which a membrane 2A is laid, with chambers 3A left in between. The chambers 3A take in liquid. Piezoelectric material 4A is laid on the membrane 2A. Applying a varying electric voltage to the piezoelectric material 4A leads to mechanical shifting thereof, taking along the membrane 2A. Thus liquid in the chambers 3A is compressed and driven out through ejection holes in the substrate 1A.
The main characteristic of micropumps is that the quantity of liquid driven out is exactly controllable and that a tiny nozzle is used, so that very small droplets form, leading to good vaporization of liquid. Since micropumps are made by a semiconductor manufacturing process, it is possible to place a large number of tiny nozzles on a small area, and costs of mass production are low. Furthermore, liquid in micropump is subject to capillarity and moves by natural force, without any need to apply pressure. This keeps the structure of flow paths and a liquid supply system simple. With exact controllability and low cost of production, micropumps have an ever increasing range of applications.
The technique of the micro-pulsation metering fuel injection system of the present invention lies in several injection units placed above the throttle valve of an engine. For the several injection units, any type of micropump is usable, with each injection unit having a plurality of micropumps. Thus fuel is ejected in tiny droplets. Exact fuantily of fuel in small droplets reach the air inlet of the throttle valve and subsequently, following the inlet pipe of the engine, enter the combustion chambers in the cylinders.
Since the present invention utilizes injection by micropumps, an intrinsic driving force in the micropumps of the injection units draws fuel, without any need to apply pressure. An external supply system works by gravitation from a higher positioned fuel tank to ensure steady supply of fuel. Pressure in supply pipes remains very low, and the risk of bursting pipes under high pressure is avoided. The micropumps of the present invention provide for ejected droplets of very small size and allow precisely to control the quantity of ejected fuel, increasing efficiency of the engine.
Furthermore, by a certain arrangement of the injection units at certain positions of the throttle body, and by electric control, every time the engine takes in air, different injection units inject fuel into certain places of the air inlet of the throttle valve. When the throttle valve is opened more widely, certain regions of the inlet manifold have a stratified distribution of fuel-to-air concentration, achieving stratified charge and lean burn process.
The present invention can be more fully understood by reference to the following description and accompanying drawings.